The present invention relates to a mold releasing agent for coating on an inner surface of a centrifugal casting mold, and in particular, relates to a mold releasing agent suitable for forming fine protrusions on the outer surface of a cast member during a casting process so as to improve the adhesion of an interface between a base material and the cast member, in a production process of a cylindrical cast member in which the outer surface thereof is cast using various base materials, such as a cylinder sleeve for an internal combustion engine, an embedded bearing, etc.
With respect to a cast member with a roughened outer surface formed by using a centrifugal casting method, a technique in which a tube member with a roughened outer surface is formed by casting after coarsely coating a facing material on an inner surface of a centrifugal casting mold, and then a wall material, a floor material, and a decorative plate member for buildings are obtained by cutting it open in the axial and circumferential direction, is disclosed in Japanese Unexamined Patent Publication No. 64-83357.
In addition, with respect to the facing material, for example, as disclosed in Japanese Unexamined Patent Publication No. 3-447, facing materials formed by combining a binder such as bentonite, kibushi clay, sodium aluminate, water glass, colloidal silica, etc., with a fiber material such as silica, chamotte, mullite, alumina, zirconia, carbon, silicon carbide, calcium silicate, potassium titanate, etc., have been proposed, in order to prevent bonding between casting metal and a metal mold or to prevent rapidly cooling of molten metal.
In recent years, as disclosed in Japanese Unexamined Patent Publication No. 9-108773, a mold releasing agent has been proposed, in which a mold releasing component; a dispersing component, and a foaming agent are mixed and foamed; the foam is filled in a metal mold in a clamped state; the mold releasing component is maintained in bubbles; and the mold releasing component is thereby prevented from separating and depositing.
In a production process of a cylindrical cast member cast using base materials, such as a cylinder sleeve for an internal combustion engine, an embedded bearing, etc., improvement in the adhesion of cast parts is required. As a method for improving the adhesion, conventionally, techniques have been proposed in which irregularities are provided on the outer surface of a sleeve by a machining process, etc., and in which irregularities are formed on an inner surface of split molds. However, these methods require a secondary process such as a machining process, resulting in subsequent increase in cost. Moreover, application of the split metal molds not only results in loss of productivity, but also requires that the metal mold be manufactured with excessively high precision and high durability in order to prevent molten metal intruding into the split mold surfaces by centrifugal force.
The present invention has been devised to solve the above-mentioned problems, and an object thereof is to provide a mold releasing agent in which a cylindrical cast member with superior adhesion in the cast part can be easily cast at low cost.
A mold releasing agent for a centrifugal casting mold of the present invention is a mold releasing agent for coating on an inner surface of an integral centrifugal casting mold, which comprises a binder, a heat insulating agent, and a solvent, the agent is in a slurry state, and is characterized by further comprising a foaming component having a foaming property (hereinafter, referred to as a foaming agent).
According to the mold releasing agent for a centrifugal casting mold constructed as above, bubbles are generated by the effect of vaporization of solvent in the mold releasing agent in a slurry state and a foaming agent, or by the effect of a foaming agent alone, and crater shaped concave portions are formed by traces in which the bubbles are released from the mold releasing agent. Then, the concave portions are transferred on the outer surface of the cast member so as to form fine protrusions, and therefore, there is no cost increase required for the operation for forming irregularities using a machining process, etc. Furthermore, since the cast member is integrally removed from the mold with the mold releasing agent of the present invention, there is no problem such as degradation in productivity due to use of split molds. Therefore, a cylindrical cast member having superior adhesion in cast parts can be easily obtained at low cost by using the mold releasing agent of the present invention.